Spectroscopic and computational characterization of lanthanide-mediated bond activation of ethylamine

Abstract

Ln (Ln = La and Ce) atom reactions with ethylamine are conducted in a pulsed laser vaporization supersonic molecular beam source. Dehydrogenation and association metal-containing species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln ethylimido species in the formula Ln(NC₂H₅) are characterized by single-photon mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and a scalar relativity correction, electron correlation, and spin-orbit coupling through multiconfiguration quasi-degenerate second-order perturbation theory for the Ce species. The MATI spectrum of lanthanum ethylimido La(NCH₂CH₃) has a single vibronic band system from the ionization of the doublet ground state with the La 6s¹ configuration, whereas that of the cerium ethylimido Ce(NCH₂CH₃) displays two vibronic band system from the ionization of the two lowest-energy spin-orbit coupling states with the Ce 4f¹6s¹ configuration. Both Ln ethylimido complexes are formed by the thermodynamically and kinetically favorable concerted dehydrogenation of the amino group. Two additional isomers of Ln(NC₂H₅) include a four-membered metallacycle Ln(NHCH₂CH₂) from the dehydrogenation of the amino and methyl groups and a three-membered cycle Ln(NHCHCH₃) from the dehydrogenation of the amino and methylene groups. The cyclic isomers are not observed experimentally as they are not populated under the experimental conditions.